This invention is in the field of dentistry and relates in particular to a measuring instrument for determining the cohesion force in two-part cone crowns.
In dentistry, cone crowns permit a firm connection of a partial, removable denture portion to the remaining teeth. Such cone crowns are formed of an outer crown and an inner crown. The latter is inserted on an appropriately filed remaining tooth and is affixed thereto. On its outer face, the inner crown has the positive shape of a cone while the outer crown has a corresponding negative conical inner surface. The cohesion force between the inner and outer crowns may be influenced by the selection of the cone angle.
As concerns the cohesion force between the inner and outer crowns, an optimal value is sought between two contradictory requirements. On the one hand, the cone crown should firmly sit while being worn which would require a small cone angle. On the other hand, it is a desideratum that the outer crown be easily removable which, in turn, calls for a sufficiently large cone angle.
Tests have shown that the cohesion force between the inner and outer crowns should be approximately 3-5N. Heretofore, the cohesion force has been determined exclusively empirically by holding the inner crown firmly with cone pliers and then pulling off the outer crown manually.
German Pat. No. 2,750,258 discloses a frictional measuring instrument for sleeve crowns, including pliers which may be inserted into the crown sleeve and with which the crown sleeve is pulled from the crown to determine the frictional forces. This known measuring instrument further has a spring scale including an inner tube, an outer tube and a tension spring as well as a removable detent mechanism which prevents the inner tube from sliding back into the outer tube when the tensioning force exceeds the frictional force retaining the sleeve in the crown and the sleeve is thus removed from the crown.